1. Technical Field
The invention relates to operator control over diesel engine exhaust particulate filter regeneration.
2. Description of the Problem
Electronic engine control systems are known which provide processor-based engine controllers that process data from various sources to develop control data for controlling certain functions of the engine. The interaction of such control systems with more general vehicle control networks, typically controller area networks (CAN), is also known. The state of development in the art is represented by the development by the Society of Automotive Engineers of several standards, most particularly the SAE J1939 standard governing vehicle control networks. The SAE J1939 standard seeks to assure, among other things, the seamless interaction of different manufacturers' engine controllers over such networks with other controllers.
The context of the present invention is the handling of diesel particulate filter (DPF) regeneration. DPF's trap Diesel Particulate Matter (DPM) includes soot or carbon, the soluble organic fraction (SOF), and ash (i.e. lube oil additives etc.). The trapping of those constituents by a DPF prevents what was once seen as black smoke billowing from a vehicle's exhaust pipe. The organic constituents of trapped DPM, i.e. carbon and SOF, are oxidized within the DPF at appropriate times and under appropriate conditions to form CO2 and H2O, which can then pass through and exit the exhaust pipe to atmosphere. The ash collects within the DPF over time, progressively aging the DPF by gradually reducing its trapping efficiency.
DPF regeneration is typically handled by the engine controller. The reasons for locating control in the engine controller stem from the fact that regeneration requires the combustion or oxidation of the carbon rich particles which have built up in the DPF. One way to regenerate a DPF involves raising the temperature in the filter to the ignition temperature of a substantial portion of the particles and supplying enough oxygen (the conventional oxidizer) or NO2 (a possible oxidizer) to the filter to support combustion. While there are several techniques used to start such combustion, most involve changing physical attributes or chemical mix of the exhaust stream into the DPF. Among the quantities that can be controlled are: temperature of the stream; the quantity of oxygen in the stream; and the amount of supplemental fuel in the stream (the supplemental fuel can have a lower combustion initiation temperature). All of these conditions can be affected by manipulating engine operation.
The rate at which trapped carbon is oxidized to CO2 is controlled not only by the concentration of NO2 or O2 but also by temperature. Specifically, there are three important temperature variables for a DPF. The first is the oxidation catalyst's “light off” temperature, below which catalyst activity is too low to oxidize HC. That temperature is typically around 180-200 degrees Celsius. The second controls the conversion of NO to NO2. This NO conversion temperature spans a range of temperatures having both a lower bound and an upper bound, which are defined as the minimum temperature and the maximum temperature at which 40% or greater NO conversion is achieved. The conversion temperature window defined by those two bounds extends from approximately 250 degrees C. to approximately 450 degrees C. The third temperature variable is related to the rate at which carbon is oxidized in the filter. Reference sources in relevant literature call that temperature the “Balance Point Temperature” (or BPT). It is the temperature at which the rate of oxidation of particulate, also sometimes referred to as the rate of DPF regeneration, is equal to the rate of accumulation of particulate. The BPT is one of the variables that is especially important in determining the ability of a DPF to enable a diesel engine to meet expected tailpipe emissions laws and/or regulations.
A typical diesel engine comprises fuel injectors for injecting fuel into the engine cylinders under control of an engine control system. The engine control system controls the duration, timing, quantity and potentially the charge shape of each pulse. These factors can be varied to control completeness of combustion, the quantity of oxygen in the exhaust, the amount of unburned fuel in the exhaust and the temperature of the exhaust. In a turbocharged diesel engine, the electronic engine control system also exercises control over turbocharger boost to vary the amount of oxygen being delivered.
Typically, a diesel engine runs relatively lean and relatively cool compared to a gasoline engine. That factor makes natural achievement of BPT problematic. Therefore, a manufacturer of a DPF for a diesel engine should strive for a design that minimizes BPT, and a diesel engine manufacturer should strive to develop engine control strategies for raising the exhaust gas temperature to temperatures in excess of BPT whenever the amount of trapped particulates exceeds some threshold that has been predetermined in a suitably appropriate manner, such as by experimentation. Using an engine control to raise exhaust gas temperature in this way is a type of regeneration.
Investigation of several methods for initiating a forced regeneration of a DPF has disclosed that retarding the start of main fuel injections seems to be the most effective way to elevate exhaust gas temperature. That method is able to increase the exhaust gas temperature sufficiently to elevate the catalyst's temperature above catalyst “light off” temperature and provide excess HC that can be oxidized by the catalyst. Such HC oxidation provides the necessary heat to raise the temperature in the DPF above the BPT.
The diesel trucking industry is developing operator interfaces for their respective 2007 EPA-mandated Diesel Particulate Filter (DPF) aftertreatment systems. These interfaces may control two basic aftertreatment operations: allow a particulate trap regeneration, and inhibit a particulate trap regeneration. Operator interfaces for such systems have typically provided only a Particulate Trap Warning lamp, and a High Exhaust Temperature System Warning lamp.
U.S. Pat. No. 6,497,095 discussed circumstances under which automatic initiation of regeneration might be inhibited. That patent provided for such inhibition in response to low fuel reserves, a consequence of the fact that most regeneration methods involve increased fuel flow.